The present invention relates to a raw material for gaskets, in each of which foam rubber layers are formed on two surfaces of a metal plate, and a method for fabricating same, and in particular to an improvement of the raw material for gaskets having a good sealing property in a wide utilization temperature range.
As prior art foam rubber coat gaskets there were known gaskets, in each of which a solution, in which rubber compound obtained by blending arrangement agents usually used for rubber such as a reinforcing agent, a vulcanizing agent, etc. and a foaming agent with natural rubber or synthetic rubber such as NBR, etc. was dissolved in a solvent, or a latex solution was vulcanized and foamed after having been applied on two surfaces of a metal plate, and gaskets, in each of which foam rubber layers were formed by applying rubber latex on two surfaces of a metal plate by means of a knife coater, a shimmer coater, a roll coater, etc., drying and vulcanizing it after having foamed it mechanically.
Further liquid foam rubber bodies were used as sealing material for flanges. In this case sealing layers were formed by applying liquid silicone rubber material directly on the flanges and foaming it, using an FIPG (Formed-In-Place-Gasket) system in which an applying robot (a pump for conveying with pressure and dosing, a nozzle for mixing and extrusion, etc., and a system controlling them) is combined therewith.
Prior art foam rubber gaskets have drawbacks that the foam layers have a small amount of resilience after exposure to a low or high temperature atmosphere and that they cannot deal with displacement of flanges and an increased gap therebetween due to vibration and applied pressure, which causes leak of liquid from a sealed vessel, because foamed material made of natural rubber or synthetic rubber such as NBR, etc. is used, as described previously.
Further, since in a foam rubber body fabricated by means of a prior art system applying liquid foam rubber for gaskets gas produced by reactions in a raw material is easily evacuated through a surface of the raw material, it is difficult to obtain a foam rubber layer having a great foam rate. For this reason the foam rubber layers are necessarily hard and therefore for dealing with great vibration of flanges or an increased gap therebetween, it is necessary to form thick foam rubber layers and a large amount of raw material is required. In addition, it is not possible to obtain thin and soft foam rubber layers.
An object of the present invention is therefore to provide a raw material for foam rubber coat gaskets at a low price, which can solve the problems described above and has a stable sealing property in a wide utilization temperature range.
In order to achieve the above object, a raw material for gaskets according to a first invention is characterized in that a liquid silicone foam rubber layer is formed on at least one surface of a metal plate.
Liquid silicone rubber used for realizing the present invention is in a liquid state or grease-like before solidification and hardened and solidified at room temperature or by heating. There is known e.g. RTV (Room Temperature Vulcanization) silicone rubber.
A raw material for gaskets according to a second invention is characterized in that a liquid silicone foam rubber layer is formed on one surface of a metal plate, while a rubber or liquid silicone foam rubber layer is formed on the other surface thereof.
A method for fabricating a raw material for gaskets according to a third invention is characterized in that a film is stretched over at least one surface of a metal plate through a predetermined gap and a liquid silicone foam rubber layer is formed by extruding liquid silicone rubber into the gap on the surface of the metal plate under the film.
In this case, the liquid silicone foam rubber layer may be formed by extruding liquid silicone rubber after having blended a foaming agent, etc. therewith and then subjecting it to a heat treatment, if necessary.
A method for fabricating a raw material for gaskets according to a fourth invention is characterized in that a liquid silicone foam rubber layer is formed by stretching a film thereon after having formed a liquid silicone rubber layer by extruding liquid silicone rubber on at least one surface of a metal plate and before bridging and foaming reactions in the silicone rubber terminate.
The problems described above have been solved by the raw material according to the present invention owing to the fact that the liquid silicone foam rubber layer is formed on at least one surface of a metal plate so as to obtain a good sealing property in a wide utilization temperature range.
Further the problems described above have been solved by the methods for fabricating a raw material for gaskets, wherein foaming and formation are effected while preventing evacuation of gas by covering the surface of liquid raw material such as rubber by a film before start of the reactions at forming the liquid silicone foam rubber layer.